/Engine/Plugins/Importers/USDImporter/Source/USDClasses/Public/USDAssetCache2.h
Returns how many assets are tracked by the asset cache in total (summing up persistent, referenced and unreferenced storage)
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintCallable, Category="USD", Meta=(CallInEditor="true")) int32 GetNumAssets() const